| Load | Deflection |
|---|
Reading a Spring Rate
Spring rate is the simplest description of a spring: the force needed to compress it one inch, found by dividing the load by the deflection it causes. A 250 pound-per-inch spring sinks one inch under 250 pounds and two inches under 500. It is the foundation of suspension tuning, because it sets how the car carries weight and reacts to bumps.
Soft Versus Stiff
A lower rate rides more comfortably and soaks up rough surfaces, but uses more travel and allows more body roll and dive. A higher rate keeps the body flatter and resists bottoming, at the cost of a harsher ride and less grip on broken pavement. The right rate balances comfort, control, and available wheel travel for how the vehicle is used.
Why the Units Matter
Spring specs come in pounds per inch, newtons per millimeter, and kilograms-force per millimeter depending on the source, and mixing them up leads to wildly wrong choices. Converting to a common unit lets you compare springs from different makers directly. Remember that spring rate at the wheel also depends on the motion ratio of the suspension linkage.
Frequently Asked Questions
Is spring rate the same as wheel rate?
No. Wheel rate is the effective rate measured at the tire, which the suspension geometry reduces from the spring rate by the square of the motion ratio.
What is a progressive spring?
One whose rate rises as it compresses, giving a soft initial response and firmer resistance deeper in travel. A single rate figure only describes a linear spring.
How do I pick a rate?
Start from the weight on the corner and the ride frequency you want, then check it against available travel. Stiffer is not always better.